Method for determining formation during drilling

Abstract

The present invention provides a formation determination method during drilling, wherein the drilling process includes a drilled part and an undrilled part, wherein the drilled part includes a logged section and an unlogged section, and the formation determination method includes: (1) establishing a three-dimensional map that characterizes the relationship between depth, drilling time, and formation velocity of different lithologies of adjacent drilled wells; (2) obtaining the lithology and drilling time corresponding to different depths of the unlogged section, and obtaining the formation velocity corresponding to different depths of the unlogged section according to the three-dimensional map of step (1), and obtaining the formation density corresponding to different depths of the unlogged section; (3) obtaining the formation velocity and formation density of the logged section; (4) obtaining corresponding synthetic seismic records using the formation velocity data and formation density data of the drilled part of the drilling process; and determining the formation lithology of the undrilled part according to the synthetic seismic records. The method can determine the formation velocity of the unlogged section and the lithology change of the undrilled section in real time without logging data.

Description

Technical Field

[0001] The invention belongs to the field of petroleum exploration, and in particular relates to a method for determining a formation during drilling. Background Art

[0002] In the actual drilling process, when drilling to a critical position, it is necessary to timely determine the current bottom hole position and determine the lithology of the formation below the bottom hole position, and then adjust the drilling fluid density and drilling technology in subsequent drilling. Therefore, it is very important to study the formation determination during the drilling process. In the area of ​​salt-bearing structure, the complexity of the salt-bearing structure causes the complexity of the lithology combination and pressure system, which brings huge difficulties to the implementation of the drilling technology and greatly limits the drilling progress and exploration and development progress in the area of ​​salt-bearing structure.

[0003] Synthetic seismic records are usually made using formation velocity, and the formation lithology is determined based on the synthetic seismic records. The most accurate method for determining formation velocity is to use acoustic logging. Generally, a well will be logged once before casing is lowered. In the same well, a layer of casing is generally lowered at a depth with the same pressure coefficient, such as the first layer of casing at 0-1400m, the second layer of casing at 1400-2000m, and the third layer of casing at 2000-3000m. Acoustic logging is performed before each layer of casing is lowered to obtain the formation velocity of 0-1400m, the formation velocity of 1400-2000m, and the formation velocity of 2000-3000m. Acoustic logging is often used to obtain formation velocity after logging, and logging requires a certain process, is not real-time, and has a certain lag.

[0004] In the absence of logging data, synthetic seismic records are generally produced by pre-stack depth migration velocity through the well, and the lithology comparison of adjacent wells is referred to for the determination of the horizon. However, in the area of ​​salt-bearing structures, the velocity field and the lithology of the formations vary greatly laterally. In the actual drilling process, due to the strong compressive stress and plastic deformation of the gypsum-salt rock, the lateral changes of various formations, especially the salt-bearing formations, will cause problems such as large changes. The accuracy of the horizon determination using the above method is difficult to accurately reflect the changes in the formation velocity and lithology of each layer being drilled.

[0005] In view of the above, how to accurately and timely determine the formation velocity and lithology changes of each layer during the drilling process is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] The present invention provides a formation determination method during drilling, so as to at least solve the problems existing in the prior art, such as difficulty in accurately and timely determining the formation velocity and lithology change of each layer.

[0007] In one aspect of the present invention, a method for determining formations during drilling is provided. The drilling process includes a drilled portion and an undrilled portion. The drilled portion includes a logged section and an unlogged section. The method for determining formations includes: (1) establishing a three-dimensional map representing the relationship between depth, drilling time, and formation velocity for different lithologies at different depths according to the drilling time and formation velocity corresponding to different lithologies at different depths in adjacent drilled wells; (2) obtaining the lithology and drilling time corresponding to different depths of the unlogged section, obtaining the formation velocity corresponding to different depths of the unlogged section according to the three-dimensional map of step (1), and obtaining the formation density corresponding to different depths of the unlogged section. (3) obtaining the formation velocity and formation density of the logged section; (4) using the formation velocity of the logged section obtained in step (3) and the formation velocities corresponding to different depths of the unlogged section obtained in step (2) as formation velocity data of the drilled portion of the well being drilled, and using the formation density of the logged section obtained in step (3) and the formation density corresponding to different depths of the unlogged section obtained in step (2) as formation density data of the drilled portion of the well being drilled; using the formation velocity data and the formation density data to obtain a synthetic seismic record corresponding to the drilled portion of the well being drilled; and determining the formation lithology of the undrilled portion based on the synthetic seismic record.

[0008] According to one embodiment of the present invention, the number of adjacent drilled wells includes at least 10 wells.

[0009] According to one embodiment of the present invention, the number of adjacent drilled wells includes 10 to 20 wells.

[0010] According to one embodiment of the present invention, the process of obtaining the formation density corresponding to different depths of the untested section includes: calculating the formation density corresponding to different depths of the untested section by using the Gardner formula.

[0011] According to one embodiment of the present invention, in step (3), the formation velocity of the logged section is measured by acoustic logging, and the formation density of the logged section is measured by density logging.

[0012] According to one embodiment of the present invention, GeoEast or Landmark is used to produce synthetic seismic records.

[0013] According to one embodiment of the present invention, the process of determining the stratigraphic lithology of the undrilled portion by using synthetic seismic records includes: obtaining synthetic seismic records of adjacent drilled wells, calibrating the stratigraphic positions of the synthetic seismic records of the adjacent drilled wells and the synthetic seismic records of the drilled portion of the well being drilled, and determining the stratigraphic lithology of the undrilled portion based on the stratigraphic position calibration.

[0014] According to one embodiment of the present invention, the well being drilled and the adjacent well having been drilled have the same lithology section combination.

[0015] According to one embodiment of the present invention, the lithology segment combination includes a lithology segment dominated by sandstone, a lithology segment dominated by mudstone, a lithology segment dominated by salt rock, and a lithology segment dominated by gypsum, which are connected in sequence.

[0016] According to one embodiment of the present invention, the formation lithology includes the type of rock.

[0017] The implementation of the present invention has at least the following beneficial effects:

[0018] According to the present invention, a three-dimensional chart of the relationship between depth, drilling time and formation velocity under different lithologies is established, and in the absence of logging data, a synthetic seismic record of the drilled part of the well being drilled can be obtained in real time. The lithology of the formation of the undrilled part of the well being drilled can be determined based on the obtained synthetic seismic record. The formation determination method during drilling of the well being drilled of the present invention has high accuracy, high reliability and certain practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A three-dimensional chart showing the relationship between depth, drilling time and formation velocity (velocity) for 14 wells drilled in a certain area under mudstone lithology established for one embodiment of the present invention (with depth (in m) as the X-axis, drilling time (in min / m) as the Y-axis, and velocity (in m / s) as the Z-axis);

[0020] Figure 2 A horizon calibration diagram according to an embodiment of the present invention includes synthetic seismic records of a drilled well A, a drilled well C, and a synthetic seismic record of a drilled portion of a well being drilled B, wherein the synthetic seismic record of the drilled portion of the well being drilled B includes a synthetic seismic record of a logged section and a synthetic seismic record of an unlogged section;

[0021] Figure 3 A is a virtual logging curve and a virtual synthetic seismic record of the unlogged section of the drilling well B produced by an embodiment of the present invention, Figure 3 B is the logging curve and synthetic seismic record produced based on the actual logging data of the unlogged section of well B being drilled. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the solutions of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0023] The method for determining formations during drilling provided by the present invention is particularly aimed at drilling in a salt-containing structural area, wherein the drilling well includes a drilled portion and an undrilled portion, and the drilled portion includes a logged section and an unlogged section. The method for determining formations comprises: (1) establishing a three-dimensional map representing the relationship between depth, drilling time and formation velocity under different lithologies according to the drilling time and formation velocity corresponding to different lithologies at different depths in adjacent drilled wells; (2) obtaining the lithology and drilling time corresponding to different depths of the unlogged section, obtaining the formation velocities corresponding to different depths of the unlogged section according to the three-dimensional map of step (1), and obtaining the formation velocities corresponding to different depths of the unlogged section (3) obtaining the formation velocity and formation density of the logged section; (4) using the formation velocity of the logged section obtained in step (3) and the formation velocities corresponding to different depths of the unlogged section obtained in step (2) as the formation velocity data of the drilled portion of the well being drilled, and using the formation density of the logged section obtained in step (3) and the formation density corresponding to different depths of the unlogged section obtained in step (2) as the formation density data of the drilled portion of the well being drilled; using the formation velocity data and the formation density data to obtain a synthetic seismic record corresponding to the drilled portion of the well being drilled; and determining the formation lithology of the undrilled portion based on the synthetic seismic record.

[0024] Specifically, a well being drilled refers to a well being drilled, including a drilled portion and an undrilled portion, wherein the drilled portion refers to a well section that has been drilled through, and the undrilled portion refers to a well section that has not been drilled through. The lithology, drilling time, depth, etc. of the drilled portion can be obtained in real time through logging during the drilling process, wherein logging refers to recording and recording well section information during the drilling process, and the well section information (logging data) includes lithology, drilling time, depth, etc. The drilled portion includes a logged section and an unlogged section, wherein the logged section refers to a well section that has been logged, and the unlogged section refers to a well section that has not been logged, wherein logging includes sonic logging, density logging, etc., and logging data is obtained through logging, and logging data includes formation velocity and formation density at different depths. There is no logging data for the unlogged section, and there is no logging data and logging data for the undrilled portion. The formation determination method during drilling provided by the present invention is used to determine the formation velocity of the unlogged section and the lithology of the undrilled portion of the well being drilled.

[0025] Specifically, the three-dimensional chart is made by taking the depth (in m) under a certain lithology as the X-axis, the drilling time (in min / m) as the Y-axis, and the formation velocity (in m / s) as the Z-axis. Among them, the drilling time refers to the pure drilling time used for drilling each unit thickness of rock formation during the drilling process. In specific implementation, the drilling time refers to the time required to drill one meter of formation, and the time is generally measured in minutes. Depth refers to the vertical distance from the ground to the formation. The three-dimensional chart provided by the present invention can reflect the relationship between the depth of the formation, the formation velocity, and the drilling time under different lithologies, and provides a good basis for determining the formation velocity of the unmeasured section and the lithology changes of the undrilled part.

[0026] In some embodiments, the number of adjacent drilled wells includes at least 10 wells, and the adjacent drilled wells refer to wells that have been drilled in the adjacent area to the well being drilled. The adjacent drilled wells have the same lithology segment combination and burial conditions as the well being drilled, and the burial conditions include, for example, the burial depth of the rock formation, etc. Generally, the drilled well data in the adjacent area will be used, and the adjacent drilled wells have corresponding synthetic seismic records, well logging data, and mud logging data, including data such as depth under different lithologies, drilling time, formation velocity, and formation density. In the specific implementation process of the present invention, the adjacent drilled wells can be 10 or more wells. The depth range of the adjacent drilled wells is generally equivalent to the depth range of the drilled part of the well being drilled, thereby improving the accuracy of the formation determination.

[0027] In some embodiments, the number of adjacent drilled wells includes 10 to 20 wells. In the specific implementation process, for example, 10 wells, 11 wells, 12 wells, 13 wells, 14 wells, 15 wells, 16 wells, 17 wells, 18 wells, 19 wells, and 20 wells.

[0028] In some embodiments, the process of obtaining the formation density corresponding to different depths of the unlogged section includes: calculating the formation density corresponding to different depths of the unlogged section by using the Gardner formula. The Gardner formula determines the formation density based on the exponential relationship between the formation velocity and the formation density. Specifically, the lithology, drilling time, and depth of the unlogged section obtained in real time by logging are matched to the three-dimensional map to obtain the formation velocity of the unlogged section, and the formation density corresponding to the unlogged section at different depths is calculated by using the Gardner formula.

[0029] In some embodiments, in step (3), the formation velocity of the logged section is measured by sonic logging. Sonic logging records the time required for the sound wave to pass through 1 meter of rock formation. The measured time is the reciprocal of the formation velocity. According to the reciprocal relationship, the formation velocity of the logged section is calculated, and a formation velocity curve can be constructed based on the formation velocity. In addition, the formation velocities corresponding to different lithologies of adjacent drilled wells at different depths can also be measured by sonic logging, and a sonic curve can be obtained based on the sonic logging data.

[0030] In some embodiments, in step (3), the formation density of the logged section is determined by density logging.

[0031] In some embodiments, GeoEast or Landmark is used to make synthetic seismic records. Specifically, a formation velocity curve and a formation density curve are respectively constructed according to the formation velocity data and the formation density data, thereby obtaining an acoustic wave curve; wave impedance data is calculated using the formation velocity data and the formation density data, and a wave impedance curve is constructed according to the wave impedance data; a synthetic seismic record corresponding to the drilled part of the well being drilled is made using the convolution of the formation reflection coefficient and the seismic wavelet, and GeoEast or Landmark is used, wherein the process of obtaining the wave impedance data and the formation reflection coefficient is carried out according to conventional methods in the art, for example, it may include: the formation velocity data v of the i-th layer is converted into the wave impedance data v of the i-th layer; i and formation density data ρ i The product of gets the wave impedance data Z of the i-th layer i , the formation reflection coefficient of the i-th layer is Z i+1 -Z i / Z i+1 +Z i , where i is greater than or equal to 0 and is an integer. The Ricker wavelet that is consistent with the main frequency of the seismic data can be used as the seismic wavelet.

[0032] Specifically, in step (4), the synthetic seismic record corresponding to the drilled portion of the well being drilled consists of a synthetic seismic record of a logged section and a synthetic seismic record of an unlogged section, wherein the synthetic seismic record of the logged section is produced based on actual logging data of the logged section, and the synthetic seismic record of the unlogged section is produced based on data of the unlogged section (i.e., virtual logging data) obtained in step (2).

[0033] In some embodiments, the process of determining the stratigraphic lithology of the undrilled portion using synthetic seismic records includes: obtaining synthetic seismic records of adjacent drilled wells, calibrating the stratigraphic positions of the synthetic seismic records of the adjacent drilled wells and the synthetic seismic records of the drilled portion of the well being drilled, and determining the stratigraphic lithology of the undrilled portion based on the stratigraphic position calibration.

[0034] Specifically, the stratum calibration can be carried out according to conventional methods in the field, for example, it may include: (1) determining the time-depth relationship between the drilled part of the well being drilled and the adjacent drilled well based on the formation velocity data of the drilled part of the well being drilled at different depths and the formation velocity data of the adjacent drilled well at different depths, and marking the stratum depth layers on the synthetic seismic records of the adjacent drilled well and the synthetic seismic records of the drilled part of the well being drilled according to the time-depth relationship; (2) determining the optimal position of the synthetic seismic records on the seismic profile by maximizing the correlation between the synthetic seismic records and the seismic wave resistance characteristics of the well bypass channel; (3) according to the wave resistance trend of the seismic profile, connecting the same stratum layers on the synthetic seismic records of the adjacent drilled well and the synthetic seismic records of the drilled part of the well being drilled together, that is, the position of the stratum layers on the seismic profile, thereby realizing the calibration of the stratum layers on the seismic profile, wherein the seismic profile is obtained according to conventional methods in the field.

[0035] Specifically, the process of determining the lithology of the undrilled portion based on the layer calibration includes: determining the bottom hole position of the drilled portion of the well being drilled according to the layer calibration result, and then determining the lithology of the undrilled portion located below the bottom hole position.

[0036] In some embodiments, the well being drilled and the adjacent well having been drilled have the same lithology interval combination.

[0037] In some embodiments, the lithology segment combination includes a lithology segment dominated by sandstone, a lithology segment dominated by mudstone, a lithology segment dominated by salt rock, and a lithology segment dominated by gypsum that are connected in sequence. Connecting in sequence means taking the ground as a reference and following the order from shallow to deep.

[0038] In some embodiments, the formation lithology includes the type of rock, including mudstone, sandstone, salt rock, gypsum, etc.

[0039] The present invention will be further described below by means of specific examples.

[0040] Example 1

[0041] This embodiment is described in detail by taking the drilling well B as an example. The drilling well B includes a drilled part and an undrilled part. The drilled part includes a logged section and an unlogged section. The formation lithology of the undrilled part is determined according to the following process:

[0042] (1) Based on the drilling time and formation velocity (velocity) corresponding to the mudstone encountered at different depths in 14 adjacent wells, a three-dimensional chart representing the relationship between depth, drilling time, and velocity was established (the three-dimensional chart corresponding to the mudstone lithology is shown in Figure 1 );

[0043] According to the above method, three-dimensional maps of the relationship between sandstone, gypsum and salt rock encountered in 14 adjacent wells at different depths, drilling time and speed were obtained respectively;

[0044] (2) obtaining the lithology and drilling time of the unlogged section in real time through logging, and determining the formation velocity corresponding to different depths of the unlogged section according to the three-dimensional chart corresponding to different lithologies established in step (1); and determining the formation density corresponding to different depths of the unlogged section through the Gardner formula;

[0045] (3) Obtaining the formation velocity of the logged section by acoustic logging; obtaining the formation density of the logged section by density logging;

[0046] (4) Based on the formation velocity data and formation density data corresponding to different depths of the drilled part of the well being drilled, GeoEast is used to produce the acoustic wave curve, velocity curve, density curve, and wave impedance curve corresponding to the drilled part, and a synthetic seismic record of the drilled part is produced based on these curves; at the same time, the synthetic seismic records of Well A and Well C are obtained, and the horizon is calibrated based on the synthetic seismic records of Well A, Well C, and the drilled part of Well B being drilled to determine the lithology of the undrilled part.

[0047] The synthetic seismic records corresponding to the drilled portion include virtual synthetic seismic records of the unlogged section and synthetic seismic records of the logged section obtained based on actual logging data.

[0048] Figure 2 The stratum calibration diagram for stratum calibration in step (4) based on the synthetic seismic records of drilled well A, drilled well C, and drilling well B (composed of synthetic seismic records of drilled well A, drilled well C, synthetic seismic records of the drilled part of drilling well B, and seismic profiles). Figure 2 From the results of the stratum calibration, it can be seen that the bottom of the drilled part of Well B is located at the bottom of lithology section E, and the undrilled part below the bottom can be determined as lithology section F, which is mainly composed of gypsum.

[0049] Figure 3 A is the virtual logging curve and virtual synthetic seismic record of the unlogged section of the drilling well B produced in step (4), wherein the virtual logging curve is produced based on the virtual logging data before the actual logging is carried out in the unlogged section; Figure 3 B is the well logging curve and synthetic seismic record produced based on the actual logging data of the unlogged section of well B being drilled. Figure 3 It can be observed that the formation determination method of the present invention can realize the construction of synthetic seismic records of unlogged sections in the absence of logging data, and the wave group characteristics of the virtual synthetic seismic records constructed by the method of the present invention are basically consistent with those of the synthetic seismic records made using actual logging curves, indicating that the synthetic seismic records constructed by the present invention have good practicality and accuracy.

[0050] The formation determination method during drilling while drilling of the present invention can construct a three-dimensional map of the depth, drilling time and speed of adjacent drilled wells under different lithologies, and obtain the formation velocity of the unmeasured section based on the three-dimensional map, thereby constructing a synthetic seismic record of the drilled part, obtaining the bottom hole position of the drilled part based on the synthetic seismic record, and timely determining the formation lithology of the undrilled part, which has a certain guiding role in the subsequent adjustment of drilling fluid density and drilling technology.

[0051] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining formations during drilling, characterized in that: The well being drilled includes a drilled portion and an undrilled portion, the drilled portion includes a logged section and an unlogged section, and the formation determination method includes: (1) Based on the drilling time and formation velocity corresponding to different lithologies at different depths of adjacent wells, a three-dimensional chart is established to characterize the relationship between depth, drilling time, and formation velocity for different lithologies; (2) obtaining the lithology and drilling time corresponding to different depths of the unmeasured well section, and obtaining the formation velocity corresponding to different depths of the unmeasured well section according to the three-dimensional map of step (1), and obtaining the formation density corresponding to different depths of the unmeasured well section; (3) Obtaining the formation velocity and density of the logged section; (4) using the formation velocity of the logged section obtained in step (3) and the formation velocities corresponding to different depths of the unlogged section obtained in step (2) as formation velocity data of the drilled portion of the well being drilled, and using the formation density of the logged section obtained in step (3) and the formation density corresponding to different depths of the unlogged section obtained in step (2) as formation density data of the drilled portion of the well being drilled; obtaining a synthetic seismic record corresponding to the drilled portion of the well being drilled using the formation velocity data and the formation density data; and determining the formation lithology of the undrilled portion based on the synthetic seismic record; The process of determining the stratigraphic lithology of the undrilled portion by using synthetic seismic records includes: obtaining synthetic seismic records of adjacent drilled wells, calibrating the stratigraphic positions of the synthetic seismic records of the adjacent drilled wells and the synthetic seismic records of the drilled portion of the well being drilled, and determining the stratigraphic lithology of the undrilled portion based on the stratigraphic calibration; the well being drilled and the adjacent drilled well have the same lithology segment combination.

2. The method for determining formations while drilling according to claim 1, characterized in that: The number of adjacent drilled wells includes at least 10 wells.

3. The method for determining formations while drilling according to claim 1, characterized in that: The number of adjacent drilled wells includes 10 to 20 wells.

4. The method for determining formations while drilling according to claim 1, characterized in that: The process of obtaining the formation density corresponding to different depths of the untested well section includes: calculating the formation density corresponding to different depths of the untested well section by using the Gardner formula.

5. The method for determining formations while drilling according to claim 1, characterized in that: In step (3), the formation velocity of the logged section is measured by acoustic logging; and / or, In step (3), the formation density of the logged section is determined by density logging.

6. The method for determining formations while drilling according to claim 1, characterized in that: Use GeoEast or Landmark to create synthetic seismic records.

7. The method for determining formations while drilling according to claim 1, characterized in that: The lithology section combination includes a lithology section dominated by sandstone, a lithology section dominated by mudstone, a lithology section dominated by salt rock, and a lithology section dominated by gypsum, which are connected in sequence.

8. The method for determining formations while drilling according to claim 1, characterized in that: The formation lithology includes the type of rock.

Images